1. Technical Field
The present disclosure relates to methods in a fab tool, and more particularly to a method for building a rule of thumb of the defect classification and methods for classifying the defect and judging the killer defect based on the rule of thumb and critical area analysis (CAA).
2. Description of Related Art
In the fab, during the semiconductor fabrication procedure, multiple processes is performed on the wafer, such priming, coating, baking, and photography processes. However, if at least a problem occurs during at least one of the processes, at least the defect is generated in the fabricated semiconductor. The defect which causes the failure of the fabricated semiconductor is called the killer defect. For example, two disconnected polygons of the pattern in the semiconductor may be shorted due to the defect, or the polygon of the pattern in the semiconductor may be separated into two disconnected polygons of the pattern due to the defect.
If the defect is the killer defect, the yield rate of the fabricated semiconductor is reduced. Fortunately, the dimension of the defect is little in the conventional semiconductor process technology, and thus the most defects are not the killer defects. However, the critical-dimension of the current semiconductor process technology is smaller than that of the conventional semiconductor process technology, and thus the defect of the semiconductor should not be neglected. Accordingly, the defect of the semiconductor should be detected, and whether the defect is the killer defect should be judged.
Referring to FIG. 1, FIG. 1 is a flow chart of a conventional method for classifying the defect and judging the killer defect. In the conventional method for classifying the defect and judging the killer defect, at step S100, the human must obtains a semiconductor image, wherein the semiconductor may have at least a defect. The semiconductor image may be photographed automatically by the scanning electron microscope (SEM), the optical microscope, or the e-beam microscope. Then, at step S102, the human must learn the typical defect type and the killer defect judgment knowledge. At step S104, the human observes at least the defect, the pattern, and the background in the semiconductor image by using his/her eyes. Next, at step S106, based on the typical defect type and the killer defect judgment knowledge, the human decides the defect type and judges whether the killer defect exists in the semiconductor according to the observation result of step S104.
Referring to FIG. 2, FIG. 2 is schematic view of a semiconductor image of an example. After the human observes the semiconductor image, the human may know that the semiconductor 2 includes a background 20, multiple polygons of a pattern 22, and defects 24. Then, based on the typical defect type and the killer defect judgment knowledge, the human will decide the each of defects 24 in the semiconductor 2 to be a short (or bridge) defect or an open defect. Both of the defects 24 are killer defects which cause the failure of the semiconductor 2.
When the killer defects of the semiconductor are judged frequently, the human must stop the semiconductor fabrication procedure, and adjust the process or equipment parameters of the processes, so as to assure the certain yield rate. The conventional method for classifying the defect and judging the killer defect can help to increase the yield rate, but it costs the fab exhaustive manpower.